Relative Risk Ratio (RRR)A measure expressed by the risk of an event in the group receiving the intervention divided by the risk in the control group. A value of one implies no effect of treatment; less than one that the intervention reduced the risk of an event; and greater than one that the occurrence of the event is increased.This measure of risk is often expressed as a percentage increase or decrease, for example ‘a 20% increase in risk’ of treatment A compared to treatment B. If the relative risk is 300%, it may also be expressed as ‘a three-fold increase’.